1. Field of the Invention
The present invention relates to a battery in which a safety valve is electrically connected to a battery element and an insulating plate is arranged between the battery element and the safety valve.
2. Description of the Related Art
In recent years, many portable electronic devices such as combination cameras (videotape recorders), digital still cameras, mobile phones, personal digital assistances, and notebook-sized personal computers have been introduced, and their size and weight have been reduced. Accordingly, as an electrical power source for such electronic devices, light-weight secondary batteries capable of providing a high energy density have been developed. Specially, since lithium ion secondary batteries in which a carbon material is used for the anode, a complex material of lithium (Li) and a transition metal is used for the cathode, and ester carbonate is used for the electrolytic solution can provide a high energy density compared to the existing lead batteries and the nickel cadmium batteries, such lithium ion secondary batteries have been in practical use widely.
FIG. 9 is a cross section showing an example of a structure of a lithium ion secondary battery in practical use. In the battery, a battery element 110 in which a cathode 111 and an anode 112 are spirally wound with a separator 113 in between is sandwiched between a pair of insulating plates 171 and 172, and is contained in a battery container 120. A safety valve 130 and a battery cover 150 are arranged at the open portion of the battery container 120 (for example, refer to Japanese Unexamined Patent Application Publication Nos. 2001-210384 and 2004-111105). In the insulating plate 171, a central aperture 171A is provided in the central portion, and a plurality of small openings 171C are provided around the central aperture 171A. The central aperture 171A is provided to derive a lead 115 of the battery element 110 to connect the lead 115 to the safety valve 130, and to let through gas generated in heating or the like to operate the safety valve 130. In addition, the central aperture 171A is used to inject an electrolytic solution into the battery container 120. The peripheral openings 171C are provided mainly to improve injection characteristics of the electrolytic solution to prevent the electrolytic solution from remaining on the insulating plate 171.